| Abstract No.: | A-C1089 |
| Country: | Canada |
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| Title: | PROSTAGLANDIN D2 PRODUCED VIA HEMATOPOIETIC-PROSTAGLANDIN D2 SYNTHASE CONTRIBUTES DETRIMENTALLY TO SPINAL CORD INJURY. |
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| Authors/Affiliations: | 1 Adriana Redensek*; 1 Ruben Lopez-Vales; 1 Samuel David;
1 The Research Institute of the McGill University Health Centre, Montreal, QC, Canada
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| Content: | Inflammatory mediators are important contributors to secondary damage caused by spinal cord injury (SCI). Limiting the inflammatory response post-injury can therefore reduce tissue damage and ameliorate functional deficits. Prostaglandin D2 (PGD2) plays a pivotal role in inflammatory responses such as allergy and asthma, however, its role in SCI has yet to be examined. Objective: To characterize the expression of the two PGD2 synthases: hematopoietic prostaglandin D2 synthase (HPGDS) and lipocalin-type prostaglandin D synthase (L-PGDS), as well as of the PGD2 receptors: DP1 and DP2, after SCI in adult mice. Also to assess the role of PGD2 produced via HPGDS in SCI.
Materials and Methods: Contusion injuries were performed on adult BALB/c, C57BL/6, HPGDS-/-, and DP1-/- mice using the Infinite Horizons Spinal Cord Impactor. Protein and RNA were extracted from injured spinal cords for Western blotting and RT-PCR, respectively. Spinal cord cross sections were used for the histological examination.
Results: The mRNA levels of HPGDS are up-regulated beginning at 3 days post-injury (dpi) and maintained for at least 28 dpi (~5 fold). DP1 mRNA levels are also slightly increased 3dpi and maintained for 21dpi (~2 fold) after SCI, whereas L-PGDS and DP2 levels are unchanged. Western blotting results show that protein levels of HPGDS are elevated beginning on day 14 and remain high until 28dpi. Protein expression for both DP1 and L-PGDS increases immediately following contusion and remain significantly elevated at day 14. In contrast, protein levels of DP2 are unchanged; but its basal expression is considerably higher than that of DP1 in uninjured tissue. The DP2/DP1 protein ratio decreases dramatically after injury, and returns to uninjured levels by day 21. Double immunofluorescence labeling revealed that HPGDS is primarily expressed in macrophages, while L-PGDS is located in oligodendrocytes. Both receptors are found in astrocytes while DP2 is also localized to neurons. We also assessed the role of HPGDS derived PGD2 after contusion injury. Administration of an inhibitor of HPGDS (HQL-79) after SCI results in significantly improved functional recovery from day 10 onwards to day 28. Knockout mice lacking the HPGDS gene also exhibited a similar improvement in functional recovery providing strong evidence to support the hypothesis that PGD2 produced by HPGDS has a detrimental effect after SCI. Knockout mice for DP1, a PGD2 receptor, show a similar functional recovery, indicating that the detrimental effects of PGD2 are likely mediated via the DP1 receptor. Further studies are underway to determine the role of the DP2 receptor as well as confirm the mechanism by which DP1 contributes to secondary damage.
Conclusion: These results indicate a detrimental role of PGD2 produced after injury. This provides a new avenue to reduce tissue loss and increase functional recovery after SCI
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